Light emitting diode and method of manufacturing thereof

ABSTRACT

The present application discloses a light emitting diode comprising a substrate; and a light emitting layer on the substrate. The light emitting layer comprises, an N-type doped layer; a quantum well active layer; and a P-type doped layer. At least one of the N-type doped layer and the P-type doped layer comprises an uneven layer adapted to concentrate light emitting from the light emitting layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage application under 35 U.S.C. § 371of International Application No. PCT/CN2015/096942 filed Dec. 10, 2015,which claims priority to Chinese Patent Application No. 201510303480.3,filed Jun. 4, 2015, the contents of which are incorporated by referencein the entirety.

FIELD

The present invention relates to electronic light emitting device, moreparticularly, to a light emitting diode and a method of manufacturingthereof.

BACKGROUND

Typically, a conventional light emitting device is of a Lambertian type.In a Lambertian type light emitting device, light is emitted in alldirections so that only a portion of the light can be utilized for itsintended purpose. The majority of the light is absorbed within thedevice. For example, the light may be emitted laterally, reflected andtrapped internally, and ultimately absorbed by various high opticalindex layers within the device. In general, about 80% of the light maybe lost in a conventional light emitting device.

SUMMARY

In one aspect, the present invention provides a light emitting diodecomprising a substrate; and a light emitting layer on the substrate. Thelight emitting layer comprises, an N-type doped layer; a quantum wellactive layer; and a P-type doped layer. At least one of the N-type dopedlayer and the P-type doped layer comprises an uneven layer adapted toconcentrate light emitting from the light emitting layer.

Optionally, the N-type doped layer, the quantum well active layer andthe P-type doped layer sequentially arranged along a direction away fromthe substrate, and the P-type doped layer comprising the uneven layer.

Optionally, the uneven layer comprises a base layer and a plurality ofridges spaced apart on the base layer, a width of a cross-section of atleast a portion of the ridge decreases gradually along emittingdirection of the light emitting layer.

Optionally, the portion of the ridge has a cross-section selected fromthe group consisting of trapezoid, triangle, arch, and semicircle.

Optionally, the plurality of ridges are integrally formed with the baselayer as a single body.

Optionally, the substrate is made of a transparent material; the lightemitting diode further comprises a reflective layer disposed on a bottomsurface of the substrate and a side wall of the light emitting diode,reflecting light towards the light emitting layer.

Optionally, the reflective layer comprises silver and/or nickel.

Optionally, the light emitting diode further comprises a buffer layersandwiched between the light emitting layer and the substrate.

Optionally, the light emitting diode further comprises a transparentprotective layer on a surface of the P-type doped layer distal to thesubstrate.

Optionally, the transparent protective layer comprises silicon oxide orpolytetrafluoroethylene.

Optionally, the light emitting diode further comprises an electrode.Optionally, the electrode comprises a P-type electrode plate on theP-type doped layer; an N-type electrode plate on the N-type doped layer;the P-type electrode plate and the N-type electrode plate are disposedalong two peripheral sides of the light emitting layer, respectively; aP-type transparent electrode connected to the P-type electrode plate; anN-type transparent electrode connected to the N-type electrode plate;and the P-type transparent electrode and the N-type transparentelectrode are spaced apart and not connected.

Optionally, the P-type transparent electrode and the N-type transparentelectrode are selected from the group consisting of comb electrode,branched electrode, toroid electrode, and spiral-wound electrode.

Optionally, the P-type electrode plate comprises a P-type ohmic contactelectrode plate in contact with the P-type doped layer and a P-typemetal electrode plate in contact with the P-type ohmic contact electrodeplate, the N-type electrode plate comprises an N-type ohmic contactelectrode plate in contact with the N-type doped layer and an N-typemetal electrode plate in contact with the N-type ohmic contact electrodeplate, the P-type transparent electrode comprises a P-type ohmic contactelectrode on the light emitting layer and a P-type transparentconductive electrode on the P-type ohmic contact electrode, and theN-type transparent electrode comprises an N-type ohmic contact electrodeon the light emitting layer and an N-type transparent conductiveelectrode on the N-type ohmic contact electrode.

Optionally, the quantum well active layer comprises a quantum barrierlayer disposed on the N-type doped layer and a quantum well layerdisposed on the quantum barrier layer.

Optionally, the P-type doped layer comprises P-doped gallium nitride,the N-type doped layer comprises N-doped gallium nitride, the quantumbarrier layer comprises gallium nitride and the quantum well layercomprises indium gallium nitride.

Optionally, the light emitting layer comprises an unintentionally dopedN-type doped layer.

In another aspect, the present invention provides a method ofmanufacturing a light emitting diode. The method comprises forming alight emitting layer on a substrate. The step of forming the lightemitting layer on the substrate comprises forming an N-type doped layer;forming a quantum well active layer on top of the N-type doped layer;forming a P-type doped layer on top of the quantum well active layer;forming a mask pattern comprising a plurality of strips disposed spacedapart on top of at least one of the N-type doped layer and the P-typedoped layer; and etching at least one of the N-type doped layer and theP-type doped layer to form a plurality of ridges having a spacing and atop surface shape corresponding to those of the plurality of strips, awidth of a cross-section of at least a portion of each of the pluralityof ridges decreases gradually along emitting direction of the lightemitting layer.

Optionally, the N-type doped layer, the quantum well active layer andthe P-type doped layer sequentially arranged along a direction away fromthe substrate, and the P-type doped layer is etched to form theplurality of ridges.

Optionally, the portion of the ridge along the emitting direction of thelight emitting layer has a cross-section selected from the groupconsisting of trapezoid, triangle, arch, and semicircle.

Optionally, the step of forming the mask pattern comprises forming amask layer on top of the P-type doped layer; forming a photoresist layeron top of the mask layer; forming a photoresist pattern corresponding tothe mask pattern; and etching the mask layer to form the mask pattern.

Optionally, the P-type doped layer is etched using an etching solution.

Optionally, the P-type doped layer comprises a P-type doped galliumnitride, and the etching solution is selected from the group consistingof hydrochloric acid solution, phosphoric acid solution, hydrofluoricacid solution, potassium hydroxide solution, aqua regia, potassiumpersulfate solution, sodium pyroborate solution, hydrogen peroxidesolution, oxalic acid solution, ammonium fluoride solution, hydroiodicacid solution, and potassium iodide solution.

Optionally, the P-type doped layer is etched by dry etching.

Optionally, the P-type doped layer comprises a P-type doped galliumnitride, and the etching gas comprises boron chloride (BCl₃) and/orchloride (Cl₂).

Optionally, the method of manufacturing a light emitting diode furthercomprises forming a transparent protective layer on the light emittinglayer.

Optionally, the transparent protective layer comprises silicon oxide orpolytetraethylene.

Optionally, prior to the step of forming the light emitting layer, themethod of manufacturing a light emitting diode further comprises forminga buffer layer on the substrate.

Optionally, the substrate is made of a transparent material, the methodof manufacturing a light emitting diode further comprises forming areflective layer disposed on a bottom surface of the substrate and aside wall of the light emitting layer, reflecting light towards thelight emitting layer.

Optionally, the step of forming the light emitting layer furthercomprises etching the P-type doped layer having the plurality of ridgesand the quantum well active layer to form a notch which extends througha portion of the P-type doped layer and a portion of the quantum wellactive layer, exposing a portion of a top surface of the N-type dopedlayer, wherein the notch is located on a peripheral side of the lightemitting layer.

Optionally, the method of manufacturing a light emitting diode furthercomprises forming an electrode.

Optionally, the electrode comprises a P-type electrode plate on theP-type doped layer, an N-type electrode plate on the portion of the topsurface of the N-type doped layer exposed by the notch, a P-typetransparent electrode connected to the P-type electrode plate, and anN-type transparent electrode connected to the N-type electrode plate,the P-type transparent electrode and the N-type transparent electrodeare spaced apart and not connected.

Optionally, the P-type electrode plate and the N-type electrode plateare disposed along two peripheral sides of the light emitting layer,respectively.

Optionally, the P-type electrode plate comprises a P-type ohmic contactelectrode plate in contact with the P-type doped layer and a P-typemetal electrode plate in contact with the P-type ohmic contact electrodeplate, the N-type electrode plate comprises an N-type ohmic contactelectrode plate in contact with the N-type doped layer and an N-typemetal electrode plate in contact with the N-type ohmic contact electrodeplate, the P-type transparent electrode comprises a P-type ohmic contactelectrode on the light emitting layer and a P-type transparentconductive electrode on the P-type ohmic contact electrode, and theN-type transparent electrode comprises an N-type ohmic contact electrodeon the light emitting layer and an N-type transparent conductiveelectrode on the N-type ohmic contact electrode.

Optionally, the step of forming the electrode comprises forming a metalpattern corresponding to the P-type electrode plate and the N-typeelectrode plate on the surface of the light emitting layer; forming atransparent electrode pattern corresponding to the P-type transparentelectrode and the N-type transparent electrode; and annealing the metalpattern and the transparent electrode pattern under a nitrogenatmosphere; forming the P-type electrode plate comprising a P-type ohmiccontact electrode plate and a P-type metal electrode plate, forming theN-type electrode plate comprising an N-type ohmic contact electrodeplate and an N-type metal electrode plate, forming the P-typetransparent electrode comprising a P-type ohmic contact electrode and aP-type transparent conductive electrode, forming the N-type transparentelectrode comprising an N-type ohmic contact electrode and an N-typetransparent conductive electrode.

Optionally, an annealing temperature in the range of 450° C. to 550° C.is used for the annealing.

Optionally, the step of forming a quantum well active layer on top ofthe N-type doped layer comprises forming a quantum barrier layer on topof the N-type doped layer; and forming a quantum well layer on top ofthe quantum barrier layer.

Optionally, the quantum well active layer comprises the quantum barrierlayer and the quantum well layer.

Optionally, the P-type doped layer comprises P-doped gallium nitride,the N-type doped layer comprises N-doped gallium nitride, the quantumbarrier layer comprises gallium nitride and the quantum well layercomprises indium gallium nitride.

Optionally, subsequent to the step of forming the quantum well activelayer and prior to the step of forming the P-type doped layer, the stepof forming the light emitting layer further comprises forming anunintentionally N-type doped layer.

BRIEF DESCRIPTION OF THE FIGURES

The following drawings are merely examples for illustrative purposesaccording to various disclosed embodiments and are not intended to limitthe scope of the present invention.

FIG. 1 is a cross-sectional view of a light emitting diode in oneembodiment.

FIG. 2A is a diagram illustrating the structure of a substrate of thelight emitting diode in one embodiment.

FIG. 2B is a diagram illustrating the structure of a light emittinglayer, a buffer layer, and a substrate in one embodiment.

FIG. 2C is a diagram illustrating the structure of a mask layer, a lightemitting layer, a buffer layer, and a substrate in one embodiment.

FIG. 2D shows the formation and exposure of a photoresist layer on topof the mask layer of FIG. 2C.

FIG. 2E shows the photoresist layer of FIG. 2D after development.

FIG. 2F shows a light emitting layer in FIG. 2E after a P-type dopedlayer being etched.

FIG. 2G shows the light emitting layer in FIG. 2F after removal of themask pattern layer.

FIG. 2H shows the light emitting layer in FIG. 2G with the addition of areflective layer.

FIG. 2I shows the light emitting layer in FIG. 2H after the formation ofa notch for disposing an electrode.

FIG. 3 is a diagram illustrating a light transmission path of a lightemitting diode in an embodiment.

FIG. 4 is a diagram illustrating a light emitting diode in plan view inanother embodiment.

FIG. 5 is a cross-sectional view of a light emitting diode in anotherembodiment.

FIG. 6 is a cross-sectional view of a light emitting diode in anotherembodiment.

FIG. 7 is a diagram illustrating a layered structure of a light emittingdiode in an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosure will now describe more specifically with reference to thefollowing embodiments. It is to be noted that the following descriptionsof some embodiments are presented herein for purpose of illustration anddescription only. It is not intended to be exhaustive or to be limitedto the precise form disclosed.

FIGS. 1, 5, and 6 are cross-sectional views of light emitting diodes insome embodiments. Referring to FIGS. 1, 5, and 6, the light emittingdiodes in the embodiments include a light emitting layer 100 disposed ona substrate 200. The light emitting layer 100 includes, sequentiallyarranged along a direction away from the substrate 200, an N-type dopedlayer 110, a quantum well active layer 120, and a P-type doped layer 130having an uneven layer structure. The uneven layer includes a base layer131 and a concentrator (e.g., a plurality of ridges spaced apart on thebase layer 131). The quantum well active layer 120 is sandwiched betweenthe N-type doped layer 110 and the P-type doped layer 130. Optionally,the P-type doped layer 130 further includes a base layer 131.Optionally, the concentrator and the base layer 131 are integrallyformed as a single body.

FIGS. 1, 5, and 6 illustrate an example in which the concentrator (e.g.,the plurality of ridges) are disposed on the P-type doped layer. In someembodiments, the concentrator can be disposed on the N-type doped layer,the P-type doped layer, or both. In some embodiments, the light emittingdiode includes a substrate 200 and a light emitting layer 100. The lightemitting layer 100 includes an N-type doped layer 110, a quantum wellactive layer 120, and a P-type doped layer 130. Optionally, at least oneof the N-type doped layer 110 and the P-type doped layer 130 includes aconcentrator, for example, an uneven layer, adapted to concentrate lightemitting from the light emitting layer 100. Optionally, both the N-typedoped layer 110 and the P-type doped layer 130 include a concentrator,e.g., an uneven layer, adapted to concentrate light emitting from thelight emitting layer 100.

The concentrator is adapted to focus and concentrate light emitting fromthe light emitting layer 100. Due to the presence of the concentrator,light emitted along directions other than the intended emittingdirection of the light emitting layer (e.g., through the light emittinglayer 100 outwardly and substantially away from the substrate 200) maybe guided back to the intended emitting direction. For example, lightemitted along a lateral direction (e.g., a direction substantiallyparallel to the surface of the light emitting layer 130) may bereflected by the concentrator so that it is redirected to the intendedlight emitting direction. Based on the above, internal light absorptionis reduced and enhanced brightness can be achieved in the light emittingdiode.

Any concentrator suitable for focusing and concentrating light may beused for making the light emitting diode. In some embodiments, theconcentrator comprises a plurality of ridges 132 spaced apart on thebase layer 131. Optionally, a width of a cross-section of at least aportion of the ridge 132 decreases gradually along emitting direction ofthe light emitting layer. The ridge 132 redirects light emitted alongdirections other than the intended emitting direction of the lightemitting layer, e.g., laterally emitted light, back to the intendedlight emitting direction. The portion of the ridge 132 can have across-section of any suitable shape. Optionally, the portion of theridge 132 has a cross-section selected from the group consisting oftrapezoid, triangle, arch, and semicircle. Optionally, the portion ofthe ridge 132 has a cross-section of trapezoid (FIG. 1). Optionally, theportion of the ridge 132 has a cross-section of triangle (FIG. 5).Optionally, the ridge 132 has a cross-section which is a combination ofan arc or semicircle on top of a rectangle (FIG. 6). Optionally, theridge 131 and the base layer 132 are integrally formed as a single body.

FIG. 3 is a diagram illustrating a light transmission path within alight emitting diode in an embodiment. Referring to FIG. 3, lightemitting out from the side walls of the ridges 132 are redirectedtowards the intended light emitting direction (e.g., through the lightemitting layer 100 outwardly and substantially away from the substrate200). Similarly, light emitted from the light emitting layer 100inwardly (e.g., towards the substrate 200) is reflected by thereflective layer 500 back to the light emitting layer 100. The reflectedlight is refracted by the light emitting layer 100 and transmittedoutwardly. The refracted light is then focused and concentrated by theconcentrator (e.g., the ridge 132) as discussed above. The top surface,the side surface and the end surface of the ridge 132 are all lightemitting surfaces. Therefore, having a ridge 132 on the light emittinglayer 100 also increases the total light emitting surface of the lightemitting diode. Consequently, a larger portion of light generated by thelight emitting diode emits through the surfaces of P-type doped layer130 outwardly. The internal light absorption is much reduced, andbrightness of the diode enhanced. Light utilization efficiency of thelight emitting diode can be greatly enhanced at least by, e.g., use ofthe concentrator and the reflective layer 500.

The substrate 200 can be made of any suitable material. For example, thesubstrate can be made of a transparent material such as sapphire orsilicon carbide. When the substrate 200 is made of a transparentmaterial, the light emitting diode may optionally further include areflective layer 500 for reflecting light towards the intended lightemitting direction, e.g., towards to the top surface of the lightemitting layer 100, through the light emitting layer 100 outwardly andsubstantially away from the substrate 200. The reflective layer 500 maybe disposed on the bottom of the substrate 200 and/or the side wall ofthe light emitting diode. Optionally, the reflective layer 500 isdisposed on both the bottom and the side wall of the light emittingdiode. Optionally, the reflective layer 500 is disposed only on thebottom of the light emitting diode. Optionally, the reflective layer 500is disposed only on the side wall of the light emitting diode.Optionally, the reflective layer 500 is disposed on top of the substrate200 (e.g., a surface of the substrate 200 proximal to the light emittinglayer 100). Optionally, the reflective layer 500 is disposed on top ofthe substrate 200 and/or the side wall of the light emitting diode. Thereflective layer 500 can be made of any suitable material. Optionally,the reflective layer 500 comprises silver and/or nickel.

The light emitting diode may further include a buffer layer 300sandwiched between the light emitting layer 100 and the substrate 200.Contamination of the light emitting layer 100 may be avoided or reducedby having a buffer layer 300. The buffer layer 300 can be made of anysuitable material, for example, aluminum nitride, aluminum galliumnitride, or gallium nitride. Optionally, the buffer layer has athickness in the range of around 1.5 μm to around 2.5 μm.

In some embodiments, the light emitting diode further includes aprotective layer 600 on top of the light emitting layer 100 to protectthe light emitting layer 100. As shown in FIG. 1, the light emittingdiode in the embodiment has a protective layer 600 disposed on the topsurface of the P-type doped layer 130. Optionally, the protective layer600 has a relatively small refractive index, e.g., ≤2.3. The protectivelayer 600 can be made of any suitable material. Optionally, theprotective layer includes silicon oxide or polytetrafluoroethylene. Theprotective layer modifies the surface of the light emitting layer 100,making the surface of the light emitting layer 100 smoother.

FIG. 4 is a diagram illustrating the plan view of a light emitting diodein another embodiment. As shown in FIG. 4, the light emitting diode inthe embodiment further includes an electrode. The electrode in theembodiment includes a P-type electrode plate 410 on the P-type dopedlayer 130, an N-type electrode plate 420 on the N-type doped layer 110,a P-type transparent electrode 430 connected to the P-type electrodeplate 410, and an N-type transparent electrode 440 connected to theN-type electrode plate 420. Optionally, the P-type transparent electrode430 and the N-type transparent electrode 440 are spaced apart and notconnected.

In some embodiments, the P-type electrode plate 410 and the N-typeelectrode plate 420 are disposed on the outer surface of the P-typedoped layer 130 (i.e., the surface distal to the substrate 200).Optionally, the P-type electrode plate 410 and the N-type electrodeplate 420 are disposed along two peripheral sides of the light emittinglayer 100, respectively. Referring to FIG. 4, the P-type electrode plate410 and the N-type electrode plate 420 are disposed on the left and theright sides of the light emitting layer 100, respectively. The P-typetransparent electrode 430 and the N-type transparent electrode 440 aredisposed between the P-type electrode plate 410 and the N-type electrodeplate 420.

In some embodiments, a plurality of light emitting diodes may beconnected in series or in parallel via a plurality of lead wires. Theelectrode plates facilitate the connection between the lead wires andthe light emitting diodes. Through the electrode plates, the lead wiresconnect the P-type electrode plate 410 and the N-type electrode plate420 to a driver circuit. The driver circuit provides voltage signalsthrough a first lead wire to the P-type electrode plate 410 and theP-type transparent electrode 430, and provides voltage signals through asecond lead wire to the N-type electrode plate 420 and the N-typetransparent electrode 440.

The electrode plate can be made of any shape. For example, the P-typetransparent electrode 430 and the N-type transparent electrode 440 canbe any of comb electrode (as shown in FIG. 4), branched electrode,toroid electrode, and spiral-wound electrode.

Referring to FIG. 1, the light emitting diode in the embodiment furtherincludes a notch on the light emitting layer 100 (e.g., the spaceoccupied by the N-type electrode plate 420). In some embodiments, thenotch extends through a portion of the P-type doped layer 130 and aportion of the quantum well active layer 120, exposing a portion of atop surface of the N-type doped layer 110. Optionally, the N-typeelectrode plate 420 can be conveniently disposed on the top surface ofthe N-type doped layer 110 exposed by the notch. As discussed above, theN-type electrode plate 420 can be disposed on a peripheral side of thelight emitting layer 100 to improve light utilization efficiency.Accordingly, the notch can also be located on a corresponding peripheralside of the light emitting layer 100.

To improve the conductive properties of the electrode, the P-typeelectrode plate 410 can optionally include a P-type ohmic contactelectrode plate in contact with the P-type doped layer and a P-typemetal electrode plate in contact with the P-type ohmic contact electrodeplate. Optionally, the N-type electrode plate includes an N-type ohmiccontact electrode plate in contact with the N-type doped layer and anN-type metal electrode plate in contact with the N-type ohmic contactelectrode plate. Optionally, the P-type transparent electrode includes aP-type ohmic contact electrode on the light emitting layer and a P-typetransparent conductive electrode on the P-type ohmic contact electrode.Optionally, the N-type transparent electrode includes an N-type ohmiccontact electrode on the light emitting layer and an N-type transparentconductive electrode on the N-type ohmic contact electrode. Optionally,the P-type ohmic contact electrode plate is connected to the P-typeohmic contact electrode. Optionally, the N-type ohmic contact electrodeplate is connected to the N-type ohmic contact electrode. Optionally,the P-type metal electrode plate is connected to the P-type transparentconductive electrode. Optionally, the N-type metal electrode plate isconnected to the N-type transparent conductive electrode.

As used herein, the term “ohmic contact electrode” or “ohmic contactelectrode plate” refers to an electrode (or an electrode plate) in whichthe characteristic of a current flowing through the electrode and thecharacteristic of a voltage across the electrode are symmetrical forwardand backward in accordance with the Ohm's law. A contact between ametal/transparent conductive material and a semiconductor is either aSchottky contact or an ohmic contact. The Schottky contact has arectification property so that a current does not flow in a reversedirection. In some embodiments, when an ohmic contact electrode is used,the contact resistance is reduced as much as possible. The term “contactresistance” is defined as a voltage to be applied so as to make a unitcurrent flow through a unit contact surface. The unit of the contactresistance is Ω·cm². Having a P-type ohmic contact electrode platebetween the P-type metal electrode plate and the P-type doped layer mayeliminate Schottky contact between the P-type metal electrode plate andthe P-type doped layer. Similarly, having an N-type ohmic contactelectrode plate between the N-type metal electrode plate and the N-typedoped layer may eliminate Schottky contact between the N-type metalelectrode plate and the N-type doped layer. Having a P-type ohmiccontact electrode between the P-type transparent conductive electrodeand the P-type doped layer may eliminate Schottky contact between theP-type transparent conductive electrode and the P-type doped layer.Having an N-type ohmic contact electrode between the N-type transparentconductive electrode and the N-type doped layer may eliminate Schottkycontact between the N-type transparent conductive electrode and theN-type doped layer. The P-type ohmic contact electrode plate, the N-typeohmic contact electrode plate, the P-type ohmic contact electrode, andthe N-type ohmic contact electrode thus facilitate the migration ofelectrons into the quantum well active layer.

The light emitting layer 100 can be made of any suitable material.Depending on the choice of light color, various material can be selectedfor making the light emitting layer 100. For example, for emitting awhite light, a P-type doped gallium nitride may be used for making theP-type doped layer 130, an N-type doped gallium nitride may be used formaking the N-type doped layer 110, and/or an indium gallium nitride orgallium nitride material may be used for making the quantum well activelayer 120.

Optionally, the quantum well active layer comprises a quantum barrierlayer disposed on the N-type doped layer and a quantum well layerdisposed on the quantum barrier layer. Optionally, the light emittinglayer 100 further includes an unintentionally doped N-type doped layer.

FIG. 7 is a diagram illustrating a layered structure of a light emittingdiode in an embodiment. Referring to FIG. 7, the light emitting diode inthe embodiment includes a P-type transparent electrode 430, a P-typedoped layer 130, an unintentionally N-type doped layer 170, a quantumwell active layer 120 including a quantum well layer and a quantumbarrier layer, an N-type doped layer 110, a buffer layer 300, asubstrate 200, and a reflective layer 500. In the embodiment of FIG. 7,the reflective layer 500 is made of nickel and/or silver, the substrate200 is made of sapphire, the buffer layer is made of gallium nitride,the quantum well layer is made of indium gallium nitride, the quantumbarrier layer is made of gallium nitride, the P-type doped layer is madeof P-type doped gallium nitride. The N-type doped layer 110 may includean unintentionally N-type doped sublayer. Optionally, an unintentionallyN-type doped sublayer 170 is disposed between the P-type doped layer 130and the quantum well active layer 120. The unintentionally N-type dopedlayer may be made of unintentionally N-type doped gallium nitride.

The P-type transparent electrode 430 may have a P-type transparentconductive electrode made of transparent metal wire or indium tin oxide.Optionally, the transparent metal wire is a nano-wire. For example, thetransparent metal wire may be a nano-wire made of silver (e.g., 900 nmthick wire) to achieve low resistance. Optionally, the P-typetransparent electrode 430 and the N-type transparent electrode 440 aremade of the same material, e.g., a silver nano-wire or indium tin oxide.The voltage between the P-type transparent electrode 430 and the N-typetransparent electrode 440 produces current. When the current passesthrough the light emitting layer 130, electrons migrate into the quantumwells of the quantum well active layer 120, trapped in a few to a fewdozen quantum wells. Energy of the electrons are quantumized, resultingin discrete energy levels. Transition of electrons between discreteenergy levels produces light.

This disclosure also provides a method of manufacturing a light emittingdiode. In some embodiment, the method includes forming a light emittinglayer on a substrate, in which the step of forming the light emittinglayer on the substrate includes forming an N-type doped layer, forming aquantum well active layer on top of the N-type doped layer, and forminga P-type doped layer on top of the quantum well active layer.Optionally, the P-type doped layer includes a base layer and aconcentrator on top of the base layer. The concentrator is adapted tofocus and concentrate light emitting from the light emitting layer. Insome embodiment, the method includes forming a light emitting layer on asubstrate, in which the step of forming the light emitting layer on thesubstrate includes forming a P-type doped layer, forming a quantum wellactive layer on top of the P-type doped layer, and forming a N-typedoped layer on top of the quantum well active layer. Optionally, theN-type doped layer includes a base layer and a concentrator on top ofthe base layer. The concentrator is adapted to focus and concentratelight emitting from the light emitting layer. Optionally, at least oneof the N-type doped layer and the P-type doped layer includes a baselayer and a concentrator on top of the base layer. Optionally, both theN-type doped layer and the P-type doped layer include a base layer and aconcentrator on top of the base layer. Optionally, the N-type dopedlayer, the quantum well active layer and the P-type doped layersequentially arranged along a direction away from the substrate, and theP-type doped layer is etched to form the plurality of ridges.

In some embodiments, the concentrator includes a plurality of ridgesspaced apart on the base layer. A width of a cross-section of at least aportion of the ridge decreases gradually along emitting direction of thelight emitting layer. The top surface, the side surface and the endsurface of the ridge all can emit light, thereby increases thebrightness of the light emitting diode. Because a width of across-section of at least a portion of the ridge decreases graduallyalong emitting direction of the light emitting layer, light emitting outfrom the side walls of the ridges 132 can be redirected towards theintended light emitting direction (e.g., through the light emittinglayer outwardly and substantially away from the substrate).

FIGS. 2B-2F illustrate a method of forming a light emitting layer in anembodiments. Specifically, FIG. 2B shows the structure of a lightemitting layer, a buffer layer, and a substrate in the embodiment. FIG.2C shows the structure of a mask layer, a light emitting layer, a bufferlayer, and a substrate in the embodiment. FIG. 2D shows the formationand exposure of a photoresist layer on top of the mask layer of FIG. 2C.FIG. 2E shows the photoresist layer of FIG. 2D after development. FIG.2F shows the light emitting layer of FIG. 2E after the P-type dopedlayer being etched.

In some embodiments, the method of forming a light emitting layerincludes forming an N-type doped layer 110 (FIG. 2B); forming a quantumwell active layer 120 a on top of the N-type doped layer 110 (FIG. 2B);forming a P-type doped layer 130 a on top of the quantum well activelayer 120 a (FIG. 2B). Optionally, the method further includes forming amask pattern 140 a comprising a plurality of strips disposed spacedapart on top of the P-type doped layer 130 a (FIG. 2C). Optionally, themethod further includes etching the P-type doped layer 130 a to form aplurality of ridges 132 having a spacing and a top surface shapecorresponding to those of the plurality of strips (FIGS. 2F and 2G). Thearea of the P-type doped layer 130 a covered by the mask pattern 140 awill not be etched, thereby forming the plurality of ridges 132.Optionally, a width of a cross-section of at least a portion of theridge decreases gradually along emitting direction of the light emittinglayer. Optionally, the plurality of ridges 132 are integrally formedwith a base layer as a single body. Optionally, the portion of the ridge132 has a cross-section selected from the group consisting of trapezoid,triangle, arch, and semicircle. The plurality of ridges 132 can have asame shape or different shapes. Optionally, the plurality of ridges 132can have a same shape for manufacturing convenience.

The mask pattern 140 a can be made of any suitable material. Optionally,the material for making mask pattern 140 a includes a hard mask filmsuch as silicon dioxide or a metal. Optionally, the step of forming themask pattern includes forming a mask layer 140 on top of the P-typedoped layer 130 a (FIG. 2C); forming a photoresist layer 150 on top ofthe mask layer 140 (FIG. 2D); forming a photoresist pattern 150 acorresponding to the mask pattern 140 a (FIG. 2E); and etching the masklayer to form the mask pattern 140 a (FIG. 2F).

The photoresist pattern 150 a can be formed by, e.g., photolithography.As shown in FIG. 2D, a mask plate 160 can be placed on top of thephotoresist layer 150. The photoresist layer 150 is then developed andexposed to obtain the photoresist pattern 150 a.

The P-type doped layer 130 a can be etched by dry etching or wetetching. Examples of dry etching methods include, but are not limitedto, reactive ion etching (RIE), deep reactive ion etching (DRIE),inductively coupled plasma etching (ICP), electron cyclotron resonanceetching (ECR), and ion beam etching, and laser machining. Variousetching gas may be used for dry etching. Examples of plasma etching gas(e.g., for dry etching a P-type doped gallium nitride) include, but arenot limited to, boron chloride (BCl₃) and chloride (Cl₂). Prior to theplasma etching procedure, the plasma etching gas is plasmatized.

Various etching solutions may be used for wet etching. Examples ofetching solutions for wet etching (e.g., wet etching a P-type dopedgallium nitride) include, but are not limited to, hydrochloric acidsolution, phosphoric acid solution, hydrofluoric acid solution,potassium hydroxide solution, aqua regia, potassium persulfate solution,sodium pyroborate solution, hydrogen peroxide solution, oxalic acidsolution, ammonium fluoride solution, hydroiodic acid solution, andpotassium iodide solution.

In some embodiments, the method of manufacturing a light emitting diodefurther includes a step of forming a transparent protective layer on thelight emitting layer. Optionally, the transparent protective layerincludes silicon oxide or polytetraethylene. Optionally, the protectivelayer has a relatively small refractive index, e.g., ≤2.3. Optionally,the protective layer is formed by a plasma-enhanced chemical vapordeposition (PECVD) process.

In some embodiments, the method of manufacturing a light emitting diodefurther includes a step of forming a buffer layer on the substrate priorto forming the light emitting layer. Optionally, the buffer layer isformed by a metal-organic chemical vapor deposition (MOCVD) process.Optionally, the buffer layer 300 is made of aluminum nitride, aluminumgallium nitride, or gallium nitride. Optionally, the buffer layer has athickness in the range of around 1.5 μm to around 2.5 μm.

In some embodiments, the substrate is made of a transparent material.Optionally, the method of manufacturing a light emitting diode canfurther include a step of forming a reflective layer 500 disposed on abottom surface of the substrate and/or a side wall of the light emittinglayer 100, reflecting light towards the intended light emittingdirection, e.g., towards to the top surface of the light emitting layer100, through the light emitting layer 100 outwardly and substantiallyaway from the substrate 200 (FIG. 2H). Optionally, the reflective layer500 is disposed on both the bottom and the side wall of the lightemitting diode. Optionally, the reflective layer 500 is disposed only onthe bottom of the light emitting diode. Optionally, the reflective layer500 is disposed only on the side wall of the light emitting diode.Optionally, the reflective layer 500 is disposed on top of the substrate200 (e.g., a surface of the substrate 200 proximal to the light emittinglayer 100). Optionally, the reflective layer 500 is disposed on top ofthe substrate 200 and/or the side wall of the light emitting diode. Thereflective layer 500 can be made of any suitable material. Optionally,the reflective layer 500 comprises silver and/or nickel. Optionally, thereflective layer 500 is formed by a magnetron sputtering process or avapor deposition process. Optionally, the reflective layer 500 has athickness around 0.5 μm. Optionally, the step of forming the reflectivelayer 500 is the last step of manufacturing the light emitting diode.Optionally, the reflective layer 500 is formed before forming theelectrode of the light emitting diode.

In some embodiments, the light emitting diode includes an electrode.Optionally, the method of forming the light emitting layer furtherincludes etching the P-type doped layer having the plurality of ridges132 and the active layer 120 a to form a notch A (FIG. 2I). Optionally,the notch A extends through a portion of the P-type doped layer and aportion of the quantum well active layer, exposing a portion of the topsurface of the N-type doped layer. Optionally, the notch is located on aperipheral side of the light emitting layer.

Based on the above, the method of manufacturing the light emitting diodein some embodiments further includes forming an electrode. Optionally,the electrode includes a P-type electrode plate on the P-type dopedlayer, an N-type electrode plate on the portion of the top surface ofthe N-type doped layer exposed by the notch, a P-type transparentelectrode connected to the P-type electrode plate, and an N-typetransparent electrode connected to the N-type electrode plate.Optionally, the P-type transparent electrode and the N-type transparentelectrode are spaced apart and not connected. Optionally, the P-typeelectrode plate and the N-type electrode plate are disposed along twoperipheral sides of the light emitting layer, respectively. Optionally,the P-type electrode plate includes a P-type ohmic contact electrodeplate in contact with the P-type doped layer and a P-type metalelectrode plate in contact with the P-type ohmic contact electrodeplate. Optionally, the N-type electrode plate includes an N-type ohmiccontact electrode plate in contact with the N-type doped layer and anN-type metal electrode plate in contact with the N-type ohmic contactelectrode plate. Optionally, the P-type transparent electrode includes aP-type ohmic contact electrode on the light emitting layer and a P-typetransparent conductive electrode on the P-type ohmic contact electrode.Optionally, the N-type transparent electrode includes an N-type ohmiccontact electrode on the light emitting layer and an N-type transparentconductive electrode on the N-type ohmic contact electrode.

Optionally, the P-type ohmic contact electrode plate is connected to theP-type ohmic contact electrode. Optionally, the N-type ohmic contactelectrode plate is connected to the N-type ohmic contact electrode.Optionally, the P-type metal electrode plate is connected to the P-typetransparent conductive electrode. Optionally, the N-type metal electrodeplate is connected to the N-type transparent conductive electrode.

In some embodiments, the step of forming the electrode includes forminga metal pattern corresponding to the P-type electrode plate and theN-type electrode plate on the surface of the light emitting layer; andforming a transparent electrode pattern corresponding to the P-typetransparent electrode and the N-type transparent electrode. Optionally,the step further includes annealing the metal pattern and thetransparent electrode pattern under a nitrogen atmosphere; and formingthe P-type electrode plate having a P-type ohmic contact electrode plateand a P-type metal electrode plate, the N-type electrode plate having anN-type ohmic contact electrode plate and an N-type metal electrodeplate, the P-type transparent electrode having a P-type ohmic contactelectrode and a P-type transparent conductive electrode, and the N-typetransparent electrode having an N-type ohmic contact electrode and anN-type transparent conductive electrode.

Optionally, an annealing temperature in the range of 450° C. to 550° C.is used for annealing. Optionally, the annealing temperature is around550° C. when the metal pattern is made of silver and the transparentelectrode pattern is made of indium tin oxide. Annealing facilitates theformation of ohmic contact layers, resulting in excellent ohmic contactbetween the electrode and the light emitting layer.

In some embodiments, the quantum well active layer includes a quantumbarrier layer and a quantum well layer. Accordingly, in someembodiments, the step of forming a quantum well active layer on top ofthe N-type doped layer includes forming a quantum barrier layer on topof the N-type doped layer; and forming a quantum well layer on top ofthe quantum barrier layer. Optionally, the P-type doped layer comprisesP-doped gallium nitride. Optionally, the N-type doped layer comprisesN-doped gallium nitride. Optionally, the quantum barrier layer comprisesgallium nitride and the quantum well layer comprises indium galliumnitride. Optionally, the P-type doped layer comprises P-doped galliumnitride, the N-type doped layer comprises N-doped gallium nitride, thequantum barrier layer comprises gallium nitride and the quantum welllayer comprises indium gallium nitride.

In some embodiments, subsequent to the step of forming the active layerand prior to the step of forming the P-type doped layer, the step offorming the light emitting layer further includes forming anunintentionally N-type doped layer 170 (FIG. 7).

The foregoing description of the embodiments of the invention has beenpresented for purposes of illustration and description. It is notintended to be exhaustive or to limit the invention to the precise formor to exemplary embodiments disclosed. Accordingly, the foregoingdescription should be regarded as illustrative rather than restrictive.Obviously, many modifications and variations will be apparent topractitioners skilled in this art. The embodiments are chosen anddescribed in order to best explain the principles of the invention andits best mode practical application, thereby to enable persons skilledin the art to understand the invention for various embodiments and withvarious modifications as are suited to the particular use orimplementation contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and their equivalentsin which all terms are meant in their broadest reasonable sense unlessotherwise indicated. Therefore, the term “the invention”, “the presentinvention” or the like does not necessarily limit the claim scope to aspecific embodiment, and the reference to exemplary embodiments of theinvention does not imply a limitation on the invention, and no suchlimitation is to be inferred. The invention is limited only by thespirit and scope of the appended claims. Moreover, these claims mayrefer to use “first”, “second”, etc. following with noun or element.Such terms should be understood as a nomenclature and should not beconstrued as giving the limitation on the number of the elementsmodified by such nomenclature unless specific number has been given. Anyadvantages and benefits described may not apply to all embodiments ofthe invention. It should be appreciated that variations may be made inthe embodiments described by persons skilled in the art withoutdeparting from the scope of the present invention as defined by thefollowing claims. Moreover, no element and component in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element or component is explicitly recited in the followingclaims.

What is claimed is:
 1. A light emitting diode, comprising: a basesubstrate; and a first semiconductor layer on the base substrate; aquantum well active layer on a side of the first semiconductor layerdistal to the base substrate; a second semiconductor layer on a side ofthe quantum well active layer distal to the first semiconductor layer; afirst electrode connected to the first semiconductor layer; a secondelectrode connected to the second semiconductor layer; and a transparentprotective layer on a side of the second semiconductor layer distal tothe base substrate; wherein at least the second semiconductor layer isan uneven layer comprising a plurality of ridges adapted to concentratelight emitting from the light emitting layer; the transparent protectivelayer is on a side of each of the plurality of ridges distal to the basesubstrate; and the first semiconductor layer and the secondsemiconductor layer are two different layers selected from an N-typedoped layer and a P-type doped layer; wherein the light emitting diodecomprises a notch extending through a portion of the secondsemiconductor layer and a portion of the quantum well active layer toexpose a portion of a top surface of the first semiconductor layer; thenotch is adjacent to peripheries of the second semiconductor layer andthe quantum well active layer; and the first electrode extends throughthe notch to be in direct contact with the portion of the top surface ofthe first semiconductor layer.
 2. The light emitting diode of claim 1,wherein the N-type doped layer, the quantum well active layer and theP-type doped layer sequentially arranged along a direction away from thebase substrate, and the P-type doped layer is the uneven layer.
 3. Thelight emitting diode of claim 1, wherein the second semiconductor layercomprises a base layer and the plurality of ridges spaced apart on thebase layer, a width of a cross-section of at least a portion of each ofthe plurality of ridges decreases gradually along emitting direction ofthe light emitting layer.
 4. The light emitting diode of claim 3,wherein each of the plurality of ridges has a cross-section selectedfrom the group consisting of trapezoid, triangle, arch, and semicircle.5. The light emitting diode of claim 3, wherein the plurality of ridgesare integrally formed with the base layer as a single body.
 6. The lightemitting diode of claim 1, wherein the base substrate is made of atransparent material; the light emitting diode further comprises areflective layer disposed on a bottom surface of the base substrate anda side wall of the light emitting diode, reflecting light towards thelight emitting layer.
 7. The light emitting diode of claim 6, whereinthe reflective layer comprises silver and/or nickel.
 8. The lightemitting diode of claim 1, further comprising a buffer layer sandwichedbetween the light emitting layer and the base substrate.
 9. The lightemitting diode of claim 1, wherein the transparent protective layer issubstantially throughout an entirety of a surface of the secondsemiconductor layer.
 10. The light emitting diode of claim 1, whereinthe transparent protective layer comprises silicon oxide orpolytetrafluoroethylene.
 11. The light emitting diode of claim 1,further comprising: a P-type electrode plate on the P-type doped layer;and an N-type electrode plate on the N-type doped layer; wherein theP-type electrode plate and the N-type electrode plate are disposed alongtwo peripheral sides of the light emitting diode, respectively; whereinthe first electrode and the second electrode are two differentelectrodes selected from a P-type transparent electrode plate and anN-type transparent electrode plate; wherein the P-type transparentelectrode is connected to the P-type electrode plate; the N-typetransparent electrode is connected to the N-type electrode plate; andthe P-type transparent electrode and the N-type transparent electrodeare spaced apart and not connected.
 12. The light emitting diode ofclaim 11, wherein the P-type transparent electrode and the N-typetransparent electrode are selected from the group consisting of combelectrode, branched electrode, toroid electrode, and spiral-woundelectrode.
 13. The light emitting diode of claim 11, wherein the P-typeelectrode plate comprises a P-type ohmic contact electrode plate incontact with the P-type doped layer and a P-type metal electrode platein contact with the P-type ohmic contact electrode plate, the N-typeelectrode plate comprises an N-type ohmic contact electrode plate incontact with the N-type doped layer and an N-type metal electrode platein contact with the N-type ohmic contact electrode plate, the P-typetransparent electrode comprises a P-type ohmic contact electrode on thelight emitting layer and a P-type transparent conductive electrode onthe P-type ohmic contact electrode, and the N-type transparent electrodecomprises an N-type ohmic contact electrode on the light emitting layerand an N-type transparent conductive electrode on the N-type ohmiccontact electrode.
 14. The light emitting diode of claim 1, wherein thequantum well active layer comprises a quantum barrier layer disposed onthe first semiconductor layer and a quantum well layer disposed on thequantum barrier layer.
 15. The light emitting diode of claim 14, whereinthe P-type doped layer comprises P-doped gallium nitride, the N-typedoped layer comprises N-doped gallium nitride, the quantum barrier layercomprises gallium nitride and the quantum well layer comprises indiumgallium nitride.
 16. The light emitting diode of claim 1, furthercomprising an unintentionally doped N-type doped layer.
 17. A method ofmanufacturing a light emitting diode, comprising forming a lightemitting layer on a base substrate, wherein the step of forming thelight emitting layer on the base substrate comprising: forming a firstsemiconductor layer on a base substrate; forming a quantum well activelayer on a side of the first semiconductor layer distal to the basesubstrate; forming a second semiconductor layer on a side of the quantumwell active layer distal to the first semiconductor layer; forming afirst electrode connected to the first semiconductor layer; forming asecond electrode connected to the second semiconductor layer; andforming a transparent protective layer on a side of the secondsemiconductor layer distal to the base substrate; wherein at least thesecond semiconductor layer is formed as an uneven layer comprising aplurality of ridges adapted to concentrate light emitting from the lightemitting layer; the transparent protective layer is formed on a side ofeach of the plurality of ridges distal to the base substrate; and thefirst semiconductor layer and the second semiconductor layer are twodifferent layers selected from an N-type doped layer and a P-type dopedlayer wherein the light emitting diode is formed to comprise a notchextending through a portion of the second semiconductor layer and aportion of the quantum well active layer to expose a portion of a topsurface of the first semiconductor layer; the notch is formed to beadjacent to peripheries of the second semiconductor layer and thequantum well active layer; and the first electrode is formed to extendthrough the notch to be in direct contact with the portion of the topsurface of the first semiconductor layer.
 18. The method of claim 17,wherein the N-type doped layer, the quantum well active layer and theP-type doped layer sequentially arranged along a direction away from thebase substrate, and the P-type doped layer is formed as the uneven layercomprising the plurality of ridges.
 19. The method of claim 17, whereineach of the plurality of ridges is formed to have a cross-sectionselected from the group consisting of trapezoid, triangle, arch, andsemicircle.
 20. The method of claim 17, wherein forming the secondsemiconductor layer comprises: forming a base layer; and forming theplurality of ridges on spaced apart on the base layer; wherein theplurality of ridges are formed so that a width of a cross-section of atleast a portion of each of the plurality of ridges decreases graduallyalong emitting direction of the light emitting layer.